V-79-10000-11230 - VSS Snapshot error. Unable to get minimum quiet time for physical volumes. Reduce the activity on these volumes, or wait and run the backup when there is less activity on the volumes.

You can also check that your VSS writers are stable by going to a command prompt and typing: vssadmin list writers.

Any writers not running and stable are in error. You can normally sort that out by performing a reboot of the server. If that doesn't work, and your OS is Windows Server 2003 you can do a search in Google for the latest VSS Rollup Patch and install it.

As the error messages said, your disk is too busy during the time of the backup to take a snapshot. You either re-schedule your backup or stop whatever job(s) that is making use of the disk at that time.